但是，人們很快發現，明膠的凝固力非常弱。膠凝化溫度隨濃度及共存鹽類的種類、濃度、溶液的pH等因素變化而變化。溶解溫度與凝固溫度相差很小，明膠在20 ℃以上就變軟了，分離微生物的劃線操作非常困難。在溫度高于25 ℃時，明膠就液化了，而大多數細菌的培養溫度都不低于25 ℃。
羅伯特·科赫的同事Walter Hesse也為同樣的問題苦惱著。一次，Walter Hesse的妻子Fannie建議他試一試用瓊脂做凝固劑，因為Fannie用瓊脂做果凍做得不錯。Walter Hesse采納了妻子的建議，發現瓊脂比明膠更適合做培養基的凝固劑，這使得在固體培養基的技術改進上邁出一大步。
Practical technical manual of finished preloaded culture medium plate (serialized 3) : development history of finished preloaded culture medium plate
The history of development of finished preloaded culture medium plate
The finished prepared petri dish, also known as ready-to-use medium, is a medium that has been sterilized and packaged, and can be used directly without weighing the sterilized medium.
The end of the 19th century, well-known German bacteriologist Koch (Robert Koch, 1843 ~ 1910) solid medium was prepared successfully, and the glass plate, to have achieved a significant change of bacteriology, greatly promote the bacteria isolation, culture and identification technology, and also promoted the development of the finished product with culture medium plate, meet the needs of the microbial detection.
In order to directly observe the shape and growth of microbes, scientists hope to grow them on solid surfaces, just as microbes grow on orange peels or potatoes. Robert Koch used boiled potatoes to grow bacteria. After that, he tried gelatinizing the culture medium with gelatin. He added gelatin to a liquid medium to melt it, then slowly poured the evenly mixed liquid onto the surface of a glass plate. When the gelatin cools and solidifies, a solid medium is formed on the surface of the glass plate. To prevent contamination with bacteria in the air, Koch also used a glass cover to separate the glass from the surrounding environment.
However, it was soon discovered that gelatin solidified very weakly. The gelation temperature varies with the concentration and the type, concentration and pH of the coexisting salts. Melting temperature and setting temperature difference is very small, gelatin in 20 ℃ above will become soft, isolation of microorganisms operation very difficult. When temperature above 25 ℃, gelatin liquefaction, and most bacteria cultivation temperature below 25 ℃.
Robert Koch's colleague, Walter Hesse, frets about the same problem. At one point, Walter Hesse's wife, Fannie, suggested that he try agar-agar as a coagulant because Fannie did a good job of making jello out of AGAR. Walter Hesse took his wife's advice and found that agar-agar was better than gelatin as a coagulant for the medium, a big step towards improving the technology of solid media.
In 1887, Richard Petri made further improvements in the Koch plate technology. Petri has designed a round double dish with a round edge, with the large plate as the lid and the small plate as the bottom. When preparing the solid medium, pour the melted medium into a small plate and cover the plate with a large plate. This is the culture medium plate that we use today.
Since then, the world famous media production companies such as Difco in the us and Oxoid in the UK have emerged. The Difco in the United States has a history of more than one hundred years. In 1979, commercial production of finished preloaded culture medium plate began. The product entered the Chinese market in 1994.
China began to develop dry medium at the end of 1950s. Up to now, there have been more than 100 medium manufacturers and more than 300 dry medium varieties. In recent decades, China's media industry has developed rapidly, and great progress has been made in the research, development and production and use of raw materials, greatly shortening the gap with developed countries.
The data shows, the earliest production of medium plate unit in China is the kuomintang central and epidemic prevention, which formed after the founding of the People's Republic of kunming institute of biological products, the preparation technology of 1:2 beef soup, add peptone AGAR, sodium chloride, strip, heating dissolves, hydrating constant volume; Add 20% sodium hydroxide to adjust the PH value to 7.6, then heat and boil it, and divide it into 500ml bottles. Each bottle is 250ml. Sterilization after the completion of the cooled to 50 degrees, in a clean environment and jars in fire protection in sterilized glass plate, wait for after cooling solidification placed at 37 degrees cultivation in 3 days, if no pollution as qualified products.
With the development of the market economy and the manual preparation on the AGAR with valid in short, the cost is higher, the production of small cottage by hand has been difficult to meet the needs of industrial production, such as time background for the finished product with culture medium plate commercialization created a feasible way. Appeared in the 1980 s, the Chinese market of domestic commercial products with medium plate, and now more and more widely used, but so far there is no market management measures and unified quality standards and control method, the commercialization of medium plate quality lack of stability and normative, directly influence the veracity and reliability of clean areas microbial test results.
With the continuous progress and optimization of the standards for the quality management of drug production and the Chinese pharmacopoeia, the detection and operation methods of microbes in clean areas are also standardized. In a word, to achieve the desired drug quality requirement, must ensure that the pharmaceutical production process clean areas microbial contamination level of authenticity, thereby must choose to meet the requirements of the quality of medium plate control over the management of the whole process of the clean area environment.